1. Field of the Invention
The present invention relates to a laminate and a multilayer printed circuit board on each of which semiconductor elements can be mounted.
The present invention, further, relates to a high density and multi-pin semiconductor device and a semiconductor mounting device capable of coping with high speed transmission with good electric characteristic and good mounting reliability.
2. Description of the Related Art
Multilayer substrates of low thermal expansibilities include a substrate having a ceramics core layer, a substrate with ceramics deposited on a copper foil by flame spraying, and so forth. The coefficients of thermal expansion of these substrates are 10 (ppm/K) or less in the planar directions thereof (in the direction of each substrate within the bonding surface thereof). The ceramics-based substrates, however, are problematic in their drillabilities in the case of forming through-holes. Meanwhile, regarding organic substance based substrates, it has been known that the coefficient of thermal expansion can be reduced by mixing an inorganic filler into a resin system. This contrivance, however, results in enlarging the elastic modulus of the substrate and is not always satisfactory for attaining lower stresses.
It has heretofore been known that a lower elastic modulus can be achieved by adding a rubber type component into the resin component of a laminate material (Japanese Patent Application Laid-open No. 100446/1986). In this case, a flexible substrate of excellent toughness is provided by rendering the resin and rubber type components miscible. This contrivance is really effective to reduce the elastic modulus of the substrate, but it tends to enlarge the thermal expansion coefficient thereof.
It has also been known to apply to a laminate the combination of a matrix resin component and another resin component which exhibits an inferior miscibility with the matrix as represented by a so-called "sea-island structure" (a phase separation structure in which a continuous matrix contains another phase (dispersed islands) existing in an independent state. The island portion is dispersed portion, and the sea portion is continuous matrix portion). As an example of such a laminate, there has been proposed a substrate in which a layer made of the resin components of the sea-island structure is formed in only the surface of the substrate, thereby attaining a lower elastic modulus and reducing thermal stresses in the case of packaging semiconductor elements on the laminate (Japanese Patent Application Laid-open No. 356995/1992). With this method, however, it is difficult to reduce the coefficient of thermal expansion of the substrate in the planar direction thereof and it has a slight effect on the characteristics of the whole substrate.
Semiconductor elements have been changed to higher integration and higher function, such as from LSI to VLSI, ULSI, and consequently elements become large in size, many in pins, fast in operating speed, much in consuming electric power.
To cope with more pins, it becomes practical to employ a grid array structure in which a connecting terminal array is provided on a mounting surface by using a multi-layered carrier substrate.
The grid array structure employs a ball grid array structure which has short length connecting terminals to realize high speed signal propagation. The ball structure as connecting terminal is effective for lower its inductance because the conductor width can be thickened. In recent years, in order to further increase the transmission speed, it is proposed that an organic material having low dielectric constant is used for the carrier substrate (U.S. Pat. No. 5,216,278).
However, since thermal expansion coefficient of organic materials are usually larger than that of semiconductor element, there is a problem in connecting reliability due to thermal stress caused by difference of thermal expansion coefficients between them.